Noticed yesterday that you have to keep the center of the cross hair box exactly on the enemy aircraft to keep the lock on. It's way more difficult than before, but not impossible. Previously the box around the cross hair was enough. This is a massive nerf to AA lock-ons non the less. I really hope it's a bug.
Maybe now we'll finally get to see a limited number added to the flares, or at least a chance for a rocket to ignore them.
It takes so long to lock on, but now you need pinpoint accuracy on a moving target with latency issues also affecting it... Its nice now I can fly around for longer ;-)